Figure 7.-- DiscocotyU salmonis, an ectoparasitic trematode 

 from the gills of trout (after Price). 



Figures, — Crossiphiala bulboglossa,i Neascus metacercaria 

 of one of the several "black spot grubs" of fish in the fathead 

 minnow, Pimephales promelas. 



seen from above and are flattened from top 

 to bottom. Four pairs of swimming legs 

 extend from their sides (fig. 9). The eggs 

 are borne in sacs at the end of the female. 

 The eggs drop off when developed, hatch, 

 and the larvae must eventually find a fish 

 or perish. There are several larval stages 

 which precede final development of the adult. 

 Other f ornns , Ergaailus , Achtheres, and Salmincola, 

 are usually found attached to the gills. 



6. Glochidia. These small larvae of some 

 of the large fresh-water clams clamp onto 

 the gills or fins of fish where they remain 

 for 10 to 20 days. Some of the fish tissue 

 grows up and over the glochidiunn (larva) 

 forming a small translucent cyst about 

 1/8 inch in diameter. If nunnerous, they 



cause considerable 

 fish. 



damage to the 



7. Bloodsuckers (leeches). Except for 

 lampreys, these are the largest external 

 parasites, sometimes reaching an inch in 

 length. There are suckers at each end of 

 the flattened, segmented body. The front 

 sucker contains the mouth with which the 

 parasite rasps a small hole in the fish skin 

 to obtain its meal of blood (fig. 10). Leeches 

 often attach near the bases of or on the fins. 

 They transmit certain protozoan parasites 

 from fish to fish through their feeding. The 

 kinds of leeches that parasitize fish do 

 not attack humans. 



Parasites of the Body Muscles 



1. Protozoa. Myxosporidian cysts contain- 

 ing many spores (fig. 3) are whitish and 



